1. Field of the Invention
The present invention relates to a photopolymerizable adhesive for adhering a minute portion and an ink jet recording head using the same. More particularly, the present invention is concerned with a photopolymerizable adhesive for adhering one member having a minute portion (e.g., convex portion or concave portion) to the other member.
The photopolymerizable adhesive can advantageously be used for forming a liquid path in which liquid (particularly, ink) generally is present for a path in which liquid passes and for a junction portion between the paths. Particularly, the photopolymerizable adhesive is effectively used for forming an ink jet recording head.
2. Related Background Art
In general, an adhesive for forming a desired space by laminating two members having a minute portion, such as convex portion or concave portion, is widely used in various fields.
Further, many kinds of articles having a photosensitive resin or photocured glass as a structural member are also known. Among them, an ink jet recording head formed by utilizing precise formation of the minute portion is disclosed in U.S. Pat. Nos. 4,417,251 and 4,558,333.
This technique is extremely effective and hence it has been put in practice.
It is disclosed in British Patent No. 2158777 (registered Apr. 20, 1988) and U.S. patent application Ser. No. 711,181 (filed Mar. 13, 1985) to form a liquid path by adhering a cover member to a substrate having a concave portion for the liquid path. These references disclose a technique in which when the cover member is adhered to the substrate with an adhesive, a joint area is adjusted to solve the problems of the adhesive.
On the other hand, U.S. Pat. Nos. 4,330,787 and 4,334,234 disclose that a cover plate having a recess portion for the liquid path is adhered to a substrate providing a discharge energy generation element. Particularly, U.S. Pat. No. 4,330,787 discloses a recording head formed by adhering a member having a minute portion such as an orifice plate providing a discharge port, that is, an assembled head formed by adhering a structural member to a substrate.
Generally, the liquid path has a minute portion having an average radius or one side of polygon of about 5 .mu.m to about 200 .mu.m and a discharge port having an average radius or one side of polygon of about 15 .mu.m to about 100 .mu.m is used. Since such a minute portion structure has a significant effect on fluidity of liquid and discharge state, it is known that the minute portion is required to be accurately formed with respect to desired dimensions. Therefore, it is necessary to form the minute portion structure by utilizing, as a typical material the photosensitive resin as a mold or a structural element.
Conventionally the following methods for producing an ink jet head, which has a process for laminating two substrates have been put in practice.
(1) A method in which an adhesive is subjected to screen printing. PA1 (2) A method in which liquid type ultraviolet rays cured resin is coated to the substrate. PA1 (3) A method in which a dry film for printed board is used as an adhesive. PA1 (4) A method in which metal having a low-melting point is subjected to metallizing, followed by diffused junction. PA1 (A) an acrylic resin having groups represented by the formulae: --COOH, --OH and --NHCH.sub.2 OR (wherein R represents a hydrogen atom or an alkyl group having 1 to 4 carbon atoms), a number average molecular weight of 3,000 to 200,000 and a glass transition temperature of at least 70.degree. C.; PA1 (B) a photopolymerizable oligomer containing at least one member selected from the group consisting of (a) an acrylate or a methacrylate of a novolak, epoxy resin, (b) an acrylate or a methacrylate of a bisphenol epoxy resin and (c) an urethane acrylate of aromatic alcohol or cycloaliphatic alcohol; and PA1 (C) a photoinitiator capable of discharging radicals with the action of activation energy rays.
The present inventors have found problems to be solved with respect to the above-mentioned conventional methods (1) to (4).
However, although the above-mentioned conventional methods (1)-(4) are unsatisfactory, they have been put in practice.
The problems of methods (1) to (4) are as follows.
In method (1), a sufficient precision cannot be obtained in view of resolution and film thickness.
In method (2), since the material has fluidity, an adhesive flows to an unrequired portion and cured there even if, for example the adhesive is ultraviolet cured. Accordingly, the adhesive flows out to the flow path, so that variations in flow path resistance and a direction of discharge may occur. Therefore, this method is undesirable for mass-production, and when a head having high density multi-discharge ports and the liquid path in which more than sixty liquid paths are formed, defective articles may be produced.
In method (3), the film-thickness of a dry film is restricted, that is, when the dry film is a photosensitive layer having a thickness of 10 .mu.m or less, production of the dry film cannot be conducted, in practice. Further, the conventional dry films do not have satisfactory properties as adhesive of which adhesive strength is high, which does not affect the shape of a minute portion or exhibit high durability.
In method (4), it is only useful for junction of metals. Further, this method cannot be used in case where heads are made of resin.
From the foregoing, the present inventors have developed an adhesive most suitable for adhering a minute portion.